1. Field of the Invention
The present invention relates to current-perpendicular-to-plane (CPP) magnetic sensing elements. More particularly, the invention relates to a magnetic sensing element capable of outputting a pulsed signal when moving over a magnetization transition region, a method for making the same, and a magnetic sensing device including the magnetic sensing element.
2. Description of the Related Art
FIG. 13 is a schematic diagram showing a state in which signal magnetic fields recorded in a recording medium which is magnetized perpendicular to the plane are detected by a conventional magnetic sensing element.
A magnetic sensing element S shown in FIG. 13 is a so-called spin-valve magnetic sensing element which is one type of giant magnetoresistive (GMR) element using a giant magnetoresistance effect and which detects recorded magnetic fields from a magnetic recording medium, such as a hard disk.
The spin-valve magnetic sensing element S includes a multilayer film in which an antiferromagnetic layer 1, a pinned magnetic layer 2, a nonmagnetic layer 3, and a free magnetic layer 4 are deposited in that order from the bottom, and a direct current is applied in the track width direction (in the X direction) of the multilayer film.
Typically, the antiferromagnetic layer 1 is composed of a Pt—Mn alloy film, the pinned magnetic layer 2 and the free magnetic layer 4 are composed of Ni—Fe alloy films, and the nonmagnetic layer 3 is composed of a Cu film.
The magnetization of the pinned magnetic layer 2 is pinned in the Y direction (in the direction of the leakage magnetic field from the recording medium, i.e., in the height direction) by an exchange anisotropic magnetic field between the antiferromagnetic layer 1 and the pinned magnetic layer 2. The magnetization of the free magnetic layer 4 is rotated by the leakage magnetic field from the recording medium.
A recording medium Mi shown in FIG. 13 is a perpendicular magnetic recording medium. The recording medium Mi travels in the Z direction.
When the magnetic sensing element S is located above the region Ma of the recording medium Mi and the leakage magnetic field from the recording medium is applied in the Y direction, the magnetization direction of the free magnetic layer 4 is changed from the X direction to the Y direction, and the electrical resistance of the magnetic sensing element is decreased. When the leakage magnetic field from the recording medium is applied antiparallel to the Y direction above the region Mb, the magnetization direction of the free magnetic layer 4 is changed toward the direction antiparallel to the Y direction, and the electrical resistance of the magnetic sensing element is increased. The leakage magnetic field is detected by a voltage change based on the change in the electrical resistance.
FIG. 14 is a diagram showing output signal waveforms of the magnetic sensing element S when the recorded magnetic fields in the region Ma to the region Mb are detected.
A leakage magnetic field in the Y direction always lies above the region Ma of the perpendicular recording medium Mi and a leakage magnetic field in the direction antiparallel to the Y direction always lies above the region Mb. Therefore, as shown in FIG. 14, the output from the spin-valve magnetic sensing element S is the integral output in which the state changes from low voltage to high voltage with the magnetization transition region Mt being the boundary. In the present signal processing technique for processing the output from the magnetic sensing element, since it is not possible to directly process the change in the integral output shown in the upper part of FIG. 14, the integral output is converted into a pulsed waveform shown in the lower part of FIG. 14 by a so-called differentiation circuit, and signal processing is then performed. However, if the output from the magnetic sensing element is passed through the differentiation circuit, noise tends to be superposed on the output signal, and the S/N ratio is deteriorated, resulting in a decrease in the net output.